Many liquid products are dispensed in combination with a gas in order to provide an atomized spray or a foam of the product. Such products may include, for example, hair sprays, anti-perspirants, deodorants, and fragrances, (in atomized form) and lotions, depilatories, mousses, and soaps (in foam form). Dispensing systems useful for dispensing such products include pressurized (aerosol) type containers, deformable containers, and manually-actuated pump mechanisms.
Negative consumer perceptions associated with aerosol containers and deformable containers for atomized or foamed products have led to a heightened interest in manually-actuated pump mechanisms. Currently commercially available pump mechanisms of this variety utilize two or more pumping chambers to separately supply the liquid product of interest along with a gas (hereinafter referred to generically as "air", the most common gas used) to a foaming or atomizing nozzle where they are combined to produce a foam or spray.
Some commercially available pump mechanisms include two or more piston and cylinder pump chambers, often concentrically arranged, which are synchronously actuated to pump the liquid and the air toward the nozzle. Such pump chambers require that a liquid-tight moving seal be maintained between the piston and the cylinder. A significant amount of friction is generated as the piston moves against the cylinder, resulting in a comparatively high pumping effort. Friction also leads to wear of the pump components, resulting in degradation of performance during the service life of the pump mechanism. Such pump mechanisms also include a comparatively large number of moving and non-moving parts which must be individually manufactured and assembled.
Piston and cylinder pump chambers are, of necessity, of constant cross section (typically cylindrical) from one end to the other so that the piston may be maintained in constant contact with the cylinder. This arrangement produces a given overall ratio of air to liquid. Although this ratio may be tailored by selection of the relative cross-sectional areas (and hence the volumes) of the air and liquid cylinders, the instantaneous ratio at any given point during the pump stoke does not equal the tailored volumetric ratio, due to the fact that air is compressible and the liquid is essentially incompressible. This results in a mixture of air and liquid with no constant air to liquid ratio during the stroke. Furthermore, liquid under pressure begins to be discharged before the air pressure can build up and overcome the pressure drop in the passage leading to the nozzle. This substandard initial instantaneous air/liquid ratio results in a poor quality spray or foam at the beginning of the dispensing cycle until the air pressure rises to the minimum level required for satisfactory performance.
In order to address the shortcomings of piston/cylinder type pump mechanisms, other commercially available pump mechanisms have been developed which utilize pump chambers with collapsible walls, such as flexible, resilient bellows. Two or more bellows are typically used to define corresponding pump chambers, often concentrically arranged, which are synchronously actuated to pump the liquid and the air toward the nozzle.
While commercially available bellows-type pumps do address the frictional shortcomings of piston/cylinder pump mechanisms, such pumps utilize bellows of relatively constant cross-section from one end to the other, and frequently similar cross-sectional profiles for both the liquid and air bellows. As such, the lack of ability to provide sufficient air at the early portion of the pump stroke as discussed above and the lack of ability to tailor the instantaneous air/liquid ratio during the pump stroke exist even in these pump mechanisms.
In addition, a further shortcoming of both the commercially available piston/cylinder pump mechanisms and multiple bellows pump mechanisms is the lack of an effective means of preventing liquid from the nozzle region from draining back downward into the air chamber during the decompression phase of the pump stroke. This drainage may build up residue and reduce the volume of the air chamber, as well as clogging valves and moving components and possibly promoting microbial growth.
Accordingly, it would be desirable to provide a manually-actuated pump mechanism for use in liquid dispensing systems which would provide for an improved air/liquid ratio profile throughout the course of a dispensing cycle. It would also be desirable to provide a manually-actuated pump mechanism for use in liquid dispensing systems which would include a reduced number of moving parts and hence be economical to produce and reliable in service.